This invention is in the field of microdisplacement transducers, by which small displacements on the order of 0.001 inch may be measured.
Several types of microdisplacement indicators have been previously invented and patented by myself and others which indicate small displacements by means of a color or intensity change of a visual indicator area. Such indicators have been commonly employed in tensile fasteners to relate changes in elongation or deformation of the fastener to external loading conditions, such that at a prescribed load or tensile stress in the fastener, the indicator will display a prominent color or brightness condition. A known shortcoming of such visual indicators is due to the subjective nature of individual color vision, in that the accuracy of the device relies on the judgement of the operator as to whether or not the proper color change has taken place. Photometric instrumentation to measure the reflectance of the indicator element can eliminate the subjective aspect of the measurement, but is in turn subject to variations due to drift, reflections or dirt present on the indicator window.